Clarify in DPDD that filterName will be included with DIASources

The DIASource record given in the DPDD (in Table 1) does not contain the filterName that the source is detected in; it is stored in the CcdVisit table because of database normalization. Accordingly, the DPDD does not explicitly specify that the alert packet will identify which filter a DIASource was detected in (Section 4.5.1).

Since we must know the filter in order to interpret the flux measurements in an alert packet, I propose we clarify that filterName will be included with each DIASource in the alerts.

Based on previous discussion in DM-8050, I believe the filterName is already included as a foreign key in the DIASource cat schema, so this change only requires a documentation change.